There are two basic types of optical fibers, tight buffered and loose tube. A loose tube type optical fiber is a composite of an optical fiber(s) loosely disposed in a buffer tube having a diameter larger than the optical fiber(s). In some types of applications it is desirable for a single buffer tube to contain a high fiber count, for example 48 fibers. Once such a buffer tube is opened up to expose the fibers, identification and grouping of the exposed fibers becomes a problem. Known prior art suggests color coding of the plastic surrounding the individual fibers and/or colored tapes grouping individual fibers in a common bundle. While colored fibers have been widely accepted by craftsmen as a means of fiber identification, colored tapes or threads used for bundle or group identification have not been without complaints. It would be desirable to group 48 fibers into four separate groups, the fibers in each group having a fiber coating of the same color as a fiber in another group. Whatever is used to create the groups must be easily removed (preferably by non-chemical means), act as a filling compound for that part of the buffer tube cavity, retain its integrity in the presence of a filling compound in the buffer tube filling the integral spaces between groups, and be inexpensive.
The prior art abounds with various disclosures to filling and flooding compounds adapted for use in telecommunications cable for both glass and copper types. Glass, by its very nature, places limitations on what filling compounds can be used and to those that can be used, how they are applied in manufacturing. Certain waxes have been found to meet most of these limitations, especially those limitations relating to applying the wax to optical fiber bundles, coloring, and removability in preparation for splicing.
For the purposes of this disclosure, the term "wax" includes, but is not limited to wax, raw wax and oil free wax and polymers, which have a modulus of elasticity that is not greater than 200,000 psi at room temperature and an elongation at breaking of not less than ten percent (10%) at room temperature and a low tear strength, i.e., removable by a fingernail. The term "filling compound" includes organic substances in which such wax-like materials are non dispersible. This invention employs wax encased groups of optical fibers and filling compound disposed inside of a buffer tube. Not only must the wax, raw wax, plus the filling compounds be drip resistant (no drip at 65.degree. to 80.degree. C.), they also must be soft enough at minus 40.degree. C. so as not to harm the fibers. The disclosed "wax" meet these requirements.
In fiber optic cable containing buffering tubes, there is the problem of antibuckling. Some sort of an antibuckling member must be provided so that the degree of dimensional change of a cable over a given temperature range is not so great, when compared to the dimensional change of the optical fiber over the same temperature range, that the optical fiber will buckle. Buckling creates severe bends, which increase attenuation. With respect to the antibuckling problem, applicants have found that by incorporating otherwise flexible elongated members, such as glass or aramid fibers, into the outermost zone of the tubular sidewall of a fiber optic buffer tube, such a structure acts to reduce buckling by causing the dimensional change of the buffer tube, from minus 40.degree. C. to plus 80.degree. C., to be so small that it does not cause optical fibers in it to bend or buckle to a degree that unacceptable optical losses occur or unacceptably high stresses are induced.
With respect to the waxes used in this invention, applicants have found that the disclosed wax can be readily heated to a fluid and applied to groups of optical fibers to form free standing composites prior to placing them in a buffer tube. Such wax/optical fiber composites do not fill all of the space delimited by the interior wall of the buffer tube not otherwise occupied by the wax optical fiber composites. Thus, an organic filling compound may be used to fill the interstitial space between composites. Such a filling compound should be one that will not cause the wax to go into a dispersed state, so as to preserve the integrity of the wax and optical fiber composite. Wax can be readily and easily colored, thus giving rise to an easy and convenient way to identify the group to which fibers in a given buffer tube belong. Colored wax permits coated optical fibers of the same color to be used in a given cable construction, yet providing a convenient device to distinguish fibers of the same color from one another. Once identification has been made, the wax is easily stripped exposing the fibers for splicing and other operations using no more a complicated tool than that of a fingernail.